Pipe Application: Urban Gas Pipeline

There are two steel pipe mainly used for urban gas pipeline, including seamless steel pipe and welded steel pipe. The intensity of seamless steel pipe is high, but it is generally the small diameter below DN200 steel pipe as the constraints of production process and cost. There are more types of welded steel pipe, according to the welding method that can be divided into straight welded steel pipe and spiral welded steel pipe two categories. Among them, straight welded steel pipe includes Longitudinal Submerged Arc Welded pipe (LSAW steel pipe), Electric Resistance Welded pipe (ERW steel pipe) steel, and so on. For urban gas line installation, Prime Steel Pipe provides Seamless steel pipe, LSAW steel pipe, ERW steel pipe, Spiral steel pipe various types of steel pipes for selection.

According to the difference of gas pressure, city gas pipeline can be divided into low pressure (no higher than 0.01MPa), medium pressure (0.01 ~ 0.4MPa), secondary pressure (0.4 ~ 1.6MPa) and high pressure (1.6 ~ 4.0MPa). Different uses, different pressures and different diameter of the pipelines determine that urban gas pipelines have different materials and different processes.

In city gas pipeline network, high pressure pipelines, sub-high-pressure pipelines and gas transmission pipe generally select steel pipe, but there are also the problem of steel pipe type choice. In recent years, LSAW steel pipe has tended to gradually replace spiral tubes in higher pressure pipelines. At present, the price of ERW steel pipe is lower than the price of spiral welded pipe, and the quality of reliability is higher than the spiral welded steel pipe, the former has a good cost performance and its application is more and more widely. There is a way to take the pipe: when the diameter ¢ ≤ 406mm, choose ERW steel pipe, when the diameter ¢> 406mm, choose LSAW steel pipe.

In the low pressure and medium pressure pipeline, PE pipe has good flexibility, and it is corrosion-resistant, pipe wall of it is smooth and other advantages. But when the pipe diameter is larger, greater than the economic limit of PE pipe diameter, you should use steel pipe. For example, the medium-pressure pipe above DN200 is mainly using ERW steel pipe.

The Material of Natural Gas Pipeline and Its Characteristics

Natural gas pipeline refers to the pipeline that transports the natural gas (including the production of oil associated gas) from the mined land or processing plant to the city gas distribution center or industrial enterprise users, also known as gas line. In the world pipeline overall length, natural gas pipe accounts for about half.

The steel pipe is the main material of the natural gas pipeline. Modern gas gathering lines and gas line are made of steel pipes those connected by welding. There are various kinds of steel pipe, including seamless steel pipe, spiral welded pipe, longitudinal welded pipe. Seamless steel pipe be appropriate for natural gas pipe that the diameter is below 529mm, and spiral welded pipe and longitudinal welded pipe are suitable for large diameter pipe.

Features of natural gas pipeline:

(1) The gas line system is a continuous closed conveyor system.
(2) From the transport, storage to the user, natural gas is with high pressure.
(3) Due to the small proportion of transported natural gas, the influence of static pressure head is much smaller than that of liquid. In design, when the height difference is less than 200 meters, the static pressure head is negligible, and the line is almost without limited by the longitudinal terrain.
(4) There is no harms of water dashing of water pipeline.
(5) Once an accident occurs, natural gas pipe is very dangerous and extensively affected. Once the natural gas pipeline rupture, it will release plenty of energy, and its tear length is longer. If the discharge of natural gas meets open fire, also easy to lead to fire.

What type of tube is used in Oil pipeline?

The tube that used in Oil pipeline is mainly carbon steel pipe, according to its manufacturing process, it can be divided into seamless steel pipe and welded steel pipe.

Seamless steel pipe has the characteristics of high strength, specifications and more features, so it is applicable to transport strong corrosive oil or transport in the high temperature conditions. The technology of seamless steel pipe is divided into hot rolling and cold drawn. As the cold drawing process will cause the material hardening, it also needs to do the corresponding heat treatment based on the specific use of pipe.

Welded steel pipe can be divided into two kinds, straight seam steel pipes (LSAW steel pipe) and spiral welded pipe (SSAW steel pipe). The process characteristics of carbon steel pipe leds the steel pipe to tend to become brittle at low temperatures, so it is mainly applied to the normal temperature pipeline, the use of pipe temperature should not exceed 300 degrees Celsius. In general, the temperature of ordinary carbon steel pipe is between 0 to 300 degrees Celsius. If using the high-quality carbon steel pipe, the temperature range can be broadened from -40 to 450 degrees Celsius. The experimental pressure of the steel pipe is generally 1.5 times of the nominal pressure. When the temperature of the material delivered does not exceed 200 degrees Celsius, the working pressure is the nominal pressure. When the temperature exceeds 200 degrees Celsius, the working pressure should be correspondingly lower than the nominal pressure.

Welded Steel Pipe Production: The Role of Welding Preheating

For welded steel pipe production, the technique means that heating the whole of the weldment or local welding area before welding is known as preheating. For those welds with higher weld strength, hardening tendency, particularly good heat-conducting property and big thickness, and when the environment temperature of welding zone is too low, it is necessary to preheating the weldment before welding. The main purpose of preheating is reducing the cooling rate and preheat temperature of welded joint. Preheating can reduce cooling rate but basically has impact on time of staying in high temperature, that is so prefect. So when welding the steel with hardening tendency, the main processing measure to reduce cooling rate and decrease hardening tendency is preheating, rather than increase the heat input.

Types of Welded Steel Pipe

1. Welded steel pipe (GB/T3092-1993) used in Low-pressure fluid delivery, also known as the general welded pipe, commonly known as black tube. It is the welded steel pipe that used to transport of water, gas, air, oil and heating steam, and other generally fluids with lower pressure. Steel pipe is divided into ordinary steel pipe and thickened pipe according wall thickness; is divided into non-threaded steel pipe (light pipe) and threaded steel pipe according to the form of pipe end. The specifications of the steel pipe are denoted by nominal caliber (mm), and the nominal caliber is the approximate value of the inner diameter. It traditionally uses inches to express, such as 11/2 and so on. Welded steel pipe used in Low-pressure fluid delivery in addition to directly use for the transport of fluid, but also is used as the original tube of galvanized welded steel pipe used in Low-pressure fluid delivery.

2. Galvanized welded steel pipe (GB/T3091-1993) used in Low-pressure fluid transmission, also known as galvanized welded steel pipe, commonly known as white tube. It is the hot dipping galvanized welded (butt weld or electrowelding) steel pipe used to transport water, gas, air oil and heating steam, warm water and other generally fluids in lower pressure. Steel pipe is divided into ordinary galvanized steel pipe and thick galvanized steel pipe according to wall thickness; is divided into non-threaded galvanized steel pipe and threaded galvanized steel pipe according to the form of pipe end. It traditionally uses inches to express, such as 11/2 and so on.

3. Ordinary carbon steel electric wire conduit (GB3640-88) is used in electrical installation ( such as the industrial and civil construction and installation of electrical equipment and other works) to protect the wire of the steel pipe.

4. LSAW steel pipe (YB242-63) is the pipe that the weld longitudinally parallel to steel pipe. It is usually divided into metric welded steel pipe, welded thin-walled pipe, transformer cooling tubing and so on.

5. SSAW steel pipe (SY5036-83) for pressurized fluid delivery is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature and welded by double-sided submerged arc welding, used for pressurized fluid delivery. The loading capacity of steel pipe is strong, welding performance is good, after a variety of strict scientific inspection and testing, it can be used safely and reliably. The diameter of steel pipe is big, transport efficiency is high, and it can save the laying of pipeline investment. So it is mainly used for conveying oil and gas pipelines.

6. ERW steel pipe used for pressurized fluid transmission (SY5038-83) is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, welded by high-frequency lap welding, used for pressurized fluid transportation. The loading capacity of steel pipe is strong, plasticity is good, and it is easy to weld and machine shaping. After a variety of rigorous and scientific inspection and testing, the pipe is safe and reliable to use, the diameter of steel pipe is large, transport efficiency is high, and it can save the laying of pipeline investment.

7. Spiral welded steel pipe (SY5037-83) used in general low-pressure fluid transmission is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, use double-sided automatic submerged arc welding or single-sided welding method to weld. It is used for water, gas, air and steam and other general low-pressure fluid transmission.

8. ERW steel pipe (SY5039-83) used in general low-pressure fluid transmission is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, use high-frequency lap welding to weld,. It is used for general low-pressure fluid delivery.

9. Spiral welded steel pipe (SY5040-83) used as pile is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, use double-sided submerged arc welding or high-frequency welding to make. It is used for civil construction, wharf, bridge and other foundation pile steel pipe.

The Hardness Test of Seamless Steel Pipe

In general, seamless steel pipe uses Brinell, Rockwell, Vickers three hardness indicators to measure the hardness.

1. Brinell hardness test

In the standard of seamless steel pipe, Brinell hardness is used most, it often use indentation diameter to represent the hardness of the material, which is both intuitive and convenient. But it is not suitable for harder or thinner steel pipes.

2. Rockwell hardness test

The Rockwell hardness test of seamless steel tubes is the same as the Brinell hardness test, they are both indentation test method. The difference is that Rockwell hardness measures the depth of indentation. Rockwell hardness test is a widely-used method currently, HRC is next only to after Brinell hardness HB in the steel pipe standard. Rockwell hardness can be applied to measure metal material from very soft to very hard, which makes up for the weakness of Brinell method. And it is simpler than the Brinell method, it can read out the hardness value directly from the hardness of the dial. However, its hardness value is not as good as the Brinell method because its indentation is small.

3. Vickers hardness test

Vickers hardness test of seamless steel tube is also an indentation test method, it can be used to measure the thin metal materials and surface layer hardness. It has the main advantages of the Brinell and Rockwell methods, and overcomes their basic shortcomings. But it is not as easy as the Rockwell method, so Vickers method is rarely used in the steel pipe standard.

Differences between LSAW Steel Pipe and Spiral Welded Pipe

Welded carbon steel pipe includes LSAW (longitudinal submerged arc welded) steel pipe and spiral welded pipe. Some people those do not very understand this industry may not know differences between the former and the latter very clearly. Don’t worry, today we will talk about this topic.

Spiral welded pipe is made by using low carbon construction steel strip or low alloy structural steel strip to roll into a tube according to a certain helix angle (called the forming angle), and then welding the seam together. It can use the narrow band steel to produce steel pipe with large diameter. Spiral welded pipe is mainly used for oil and natural gas pipeline, its specifications are expressed by outer diameter * wall thickness. Spiral welded pipe with also includes single-sided welding and double-sided welding.

LSAW steel pipe is made by using strip steel as raw materials and doing longitudinal welded in the high-frequency welding equipment(hence the name due to the weld forms a straight line). In accordance with the use of different, there are different following production process (can be divided into scaffolding tube, fluid tube, wire casing, bracket tube, fence tube, etc.).

From the production process, the production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and it develops rapidly. But the strength of the spiral welded pipe is generally higher than that of the LSAW steel pipe. Spiral welded pipe with larger diameter can be produced with the narrow billet, and the pipe with different diameter can also be produced with the same width. However, compared with the same length of the LSAW steel pipe, the weld length of spiral welded pipe increased by 30 to 100%, and the production rate of it is low.

From the welding process, the welding method of spiral welded pipe and straight seam welded pipe is consistent. But the straight seam welded pipe will inevitably have a lot of T-shaped welds, so the probability of appearing welding defects are greatly improved. And the welding residual stress at TIG welding is large, the weld metal is often in three-dimensional stress condition, which increases the possibility of producing crack. Moreover, according to the submerged arc welding process, each weld should have starting arc place and arc blowout place, but each LSAW steel pipe can not achieve the conditions in the welding ring, which may cause there are more welding defects in the arc blowout place.